Photochemistry of α,β-Unsaturated Thiones: Cycloaddition to Electron-Deficient Olefins from Higher Excited States

Article abstract of DOI:10.1021/jo00237a021

Electron-deficient olefins add to thioenone 1 upon ??^* excitation.Cycloaddition occurs to the thiocarbonyl chromophore preferentially from the less-hindered side to yield thietanes.Thietane formation is stereospecific and regioselective.This addition has been inferred to originate from the second excited singlet, S₂(??^*), state.The exciplex intermediacy has been inferred from the dependence of the fluorescence quenching rate constant on the electron-acceptor properties of the olefin.The observed site specificity and regioselectivity are rationalized on the basis of PMO theory.The observed photochemical behavior of thioenone is different from that of enones.